Multiple organ dysfunction is a life threatening syndrome that affects a considerable proportion of patients after resuscitation from hemorrhagic shock (HS). Lung is a critical target in this insidious process. Histopathologic and physiologic studies have shown that structural and functional changes in the pulmonary endothelium contribute significantly to the pathogenesis of post-HS lung injury. Injury to lung appears to be secondary to systemic events including delivery to the pulmonary circulation of activated neutrophils, cytokines and bacteria (and their toxins) via translocation from ischemic gut and/or liver. The molecular mechanisms responsible for pulmonary damage in post HS lung injury remain unclear but a role for an imbalance between free radicals and cellular defense mechanisms is apparent. We propose that the molecular determinants for enhanced sensitivity of the lung to pro-inflammatory stimuli during resuscitation arise early in the course of HS within resident cells of the alveolar capillary barrier. We theorize that adaptive responses to HS, including increased intrapulmonary synthesis of NO, result in endothelial cell metabolic changes thereby initiating a sequence of events including apoptosis. These compensatory responses may initially be critical components of pulmonary defense, but in the transition to more severe HS, they become maladaptive. The molecular events leading to apoptosis become unbalanced due to excessive production of iNOS-derived NO in the presence of oxidative stress (enhanced superoxide anion production and decreased intracellular thiols). Accordingly, SPECIFIC AIMS are to determine: I. a protective role for metallothionein (MT) in modifying pulmonary endothelial cell injury after resuscitation from HS or hepatic ischemia/reperfusion (I/R) in MT knockout and transgenic mice; II. a contributory role for iNOS-derived NO in post-HS and IR lung injury in iNOS knockout mice; III. the molecular mechanism and intracellular signaling pathways in which NO causes endothelial cell damage and apoptosis during oxidative stress in cultured murine lung endothelial cells(MLEC); and IV. effects of NO on novel gene expression in lung tissue and MLEC during oxidative stress by RT-PCR-differential display.